JPH0157166B2 - - Google Patents

Abstract

The invention relates to polyoxymethylene fibrids with a reduced specific viscosity of 0.4 to 2.0 dl/g, a specific surface area of 50 to 200 m2/g and a freeness of 30 DEG to 80 DEG SR. The fibrids are produced by flash-evaporation of a superheated solution of the polymer, a mixture of 50-95% by weight of a lower alcohol with 1-4 C atoms and 5-50% by weight of water being used as the solvent and are suitable for the production of paper.

Description

DETAILED DESCRIPTION OF THE INVENTION Fibrids are longitudinally oriented, cellulose-like structures, i.e. fibers and filaments with finite but unequal lengths, irregular density, cracked surfaces and a high degree of branching. be done. Due to its structure, it is particularly suitable for the production of paper.

The production of such fibrids is described, for example, in German Patent Specification No. 1290040. According to this method, a woven filament is first produced, which is then cut into staple lengths, the staple fiber pieces are suspended in a liquid, and the pieces present in the suspension are chopped in a manner known per se. The term plexus filament here refers to a number of oriented molecular filaments thinner than 2μ thick, interconnected and separated from each other and preferably oriented in the direction of the longitudinal axis at irregular intervals along the length. The present invention relates to a thread-like product consisting of a crystalline plastic having a three-dimensional network consisting of film- or sliver-like fibrids, which is virtually free of tunnel-like grooves and cavities.

This plexus filament and its manufacture are described in Belgian Patent Specification No. 568,524. In this case, in order to produce plexi filaments, a solution of the autogenous or synthetic polymer under high pressure is forced through an orifice at a temperature above the boiling point of the solvent measured at normal pressure into a chamber under low pressure. do. This production of plexus filaments is also called flop spinning or expansion spinning.

Polyoxymethylene can also be produced in this way into plexus filaments and then chopped into fibrids. Neutral solvents, in particular methylene chloride, ethylene chloride, acetonitrile and methyl ethyl ketone, are used in Belgian Patent Specification No. 568,524 as solvents for producing plexus filaments. As tests have shown, significantly lower polymer concentrations, e.g. 1% by weight in methyl ethyl ketone
Even at a heavy body concentration of , only plexus filaments are formed without fibrids. Since clustered filaments are not suitable for paper production, they have to be processed into fibrids in a second step according to the above-mentioned German Patent Specification No. 1290040, which makes the process expensive. The polyoxymethylene fibrids obtained in this way have a particularly low specific surface area and a low degree of freeness, and the paper produced therefrom has a relatively low strength.

Fibrous products are likewise obtained when polyoxymethylene is precipitated from its solution by cooling the solution or by discharging it onto a precipitating agent (see German Patent Application No. 1241116). However, paper with satisfactory properties cannot be produced from this method. This is because the fibers are very short and thick and are heavily contaminated by two-dimensional film-like structures.

Finally, it is also known from Japanese Patent Publication No. 46-41110 that fibers can be obtained by stirring polyoxymethylene solutions. However, this process is too time-consuming and also unsuitable for industrial use due to its low yield.

The object of the present invention is to provide polyoxymethylene fibrids and a process for their preparation which do not have, or at least substantially do not have, the disadvantages of the state of the art and in particular the disadvantages mentioned above.

The subject of the invention is therefore a homopolymer of formaldehyde or a cyclic oligomer of formaldehyde, or a copolymer of formaldehyde or a cyclic oligomer of formaldehyde,
In this case, in addition to the oxymethylene units, further oxyalkylene units having at least 2 carbon atoms are included, and the copolymer is prepared in a superheated solution of the polymer having primary alcohol end groups as a solvent. Lower alcohol 55~90% by weight and water 10~
reduced specific viscosity (140 °C in butyrolactone containing 2% by weight of diphenylamine) formed by flash evaporation in the presence of a mixture consisting of 45% by weight of
(measured at a concentration of 0.5g/100ml) 0.4 to 2.0
dl/g ^-1 preferably 0.6 to 1.20 dl x g ^-1 , specific surface area (measured with argon by BET method)
50 to 200 m ² /g, preferably 70 to 110 m ² /g and freeness (measured by Schopper-Riegler method) 30-
It is a polyoxymethylene fibride having an SR of 80°, preferably 40 to 70°.

Furthermore, the present invention provides a method for producing the polyoxymethylene fibride by flash-evaporating the superheated solution of the polymer through a nozzle into a low pressure region, in which a lower alcohol having 1 to 4 C-atoms is used as a solvent. The process is characterized in that it uses a mixture consisting of 50-95% by weight and 5-50% by weight of water.

Suitable materials for producing the fibrids according to the invention are known polyoxymethylenes. By this product is meant formaldehyde or a cyclic oligomer of formaldehyde, such as a homoheavy form of trioxane, whose hydroxy end groups have been chemically stabilized against decomposition by known methods, for example by etherification or esterification.

Furthermore, the term polyoxymethylene also includes according to the invention copolymers of formaldehyde or cyclic oligomers of formaldehyde, preferably trioxane, in which case the copolymers contain, in addition to the oxymethylene units, at least 2 preferably have oxyalkylene units with 2 to 8 and especially 2 to 4 adjacent carbon atoms and have primary alcohol end groups. The comonomer content in the copolymer is advantageously between 0.1 and 20, preferably between 0.5 and 20.
10% by weight, especially 0.7-5% by weight.

As compounds suitable for copolymerization with formaldehyde or cyclic oligomers of formaldehyde, preferably with trioxane, inter alia cyclic ethers, preferably cyclic ethers having 3, 4 or 5 ring members and/or cyclic acetals different from trioxane, preferably 5 to 11 preferably 5, 6 or 7
Formals and/or linear polyacetals having 5 ring members are preferably used.

As comonomers for trioxane, in particular those of the formula (In the formula (A) R ¹ and R ² are the same or different and each is a hydrogen atom, preferably 1-6, preferably 1, 2, 3
or an aliphatic alkyl or phenyl residue having 4 carbon atoms, and (a) x is 1, 2 or 3 and y is zero, or (b) x is zero,
y is 1, 2 or 3 and z is 2, or (c) x is zero, y is 1 and z is 3, 4, 5
or 6, or (B) R ¹ is 2-6, preferably 2,
means an alkoxymethyl or phenoxymethyl residue having 3 or 4 carbon atoms, in which case x is 1 and y is zero or y and z are 1
and R ² has the meaning given above) are suitable. Cyclic ethers include epoxides such as ethylene oxide, propylene oxide,
Styrene oxide, cyclohexene oxide, oxacyclobutane and phenyl glycidyl ether are used. Among the cyclic acetals,
aliphatic or cycloaliphatic α,ω-diols having 2 to 8 preferably 2, 3 or 4 carbon atoms, the carbon chain of which can be interrupted by oxygen atoms at intervals of 2 carbon atoms; Cyclic formals such as glycol formals (1,3-oxolane),
Propanediol formal (1,3-dioxane), butanediol formal (1,3-dioxebane), and diglycol formal (1,3-dioxane),
3,6-trioxocane) and 4-chloromethyl-1,3-dioxolane and hexanediol formal (1,3-dioxonane) are suitable. Unsaturated formals such as butenediol formal (1,3-dioxacycloheptene-[5]) are used.

Suitable linear polyacetals are homo- or copolymers of the cyclic acetals defined above as well as linear condensates of aliphatic or cycloaliphatic α,ω-diols and aliphatic or thiol aldehydes, preferably aldehydes. In particular linear formal homopolymers of aliphatic α,ω-diols having 2-8 preferably 2-4 carbon atoms, such as poly(1,3-dioxolane), poly-(1,3-dioxane) and Poly-(1,3-dioxepane) is used.

Additional comonomers for trioxane include compounds which optionally have a large number of polymerizable groups in the molecule, and compounds which optionally also have a large number of polymerizable groups in the molecule, such as alkylglycidyl formals,
Polyglycol diglycidyl ethers, alkanediol diglycidyl ethers or bis(alkanetriol)-triformals are used in particular in amounts of 0.05 to 5% by weight, preferably 0.1 to 2% by weight, based on the total monomer amount. Such additional comonomers are described, for example, in German Patent Application No. 2101817
listed in the number.

The reduced specific viscosity (RSV-value) of the polyoxymethylene used according to the invention and of the fibrids obtained therefrom is generally between 0.4 and 2.0 dl·g ^-1 (in butyrolactone containing 2% by weight of diphenylamine).
(measured at 140°C at a concentration of 0.5g/100ml).

The melting point of polyoxymethylene microcrystals is 140-180℃
Preferably it is in the range 150° C. to 170° C. and its density is 1.38 to 1.45 g.ml ⁻¹ , preferably 1.40 to 1.43 g.ml ⁻¹ (measured according to DIN 53479).

If polymers with RSV values lower than those mentioned above are used, fibrids will certainly also form. Nevertheless, it is relatively short and mixed with a significant amount of non-fibrous parts. Therefore the polymer
Since the fiber length, slenderness ratio and degree of branching of the fibrids can be adjusted via the RSV value, the preferred range depends on the field of use of the fibrids.
At RSV values higher than those mentioned above, the risk of forming plexus filaments or predominantly two-dimensional film-like structures increases.

The preferably binary or ternary oxymethylene copolymers used according to the invention are prepared by polymerizing the monomers in a known manner in the presence of a cationically active catalyst at temperatures of 0 to 100°C, preferably 50 to 90°C. (see US Pat. No. 3,027,352). Catalysts used in this case are, for example, Lewis acids such as boron trifluoride and antimony pentafluoride and complex compounds of Lewis acids, preferably etherified products such as boron trifluoride diethyl etherate and boron trifluoride-di-tert-butyl etherate. be done. Also suitable are protic acids such as perchloric acid and salt-like compounds such as triphenylmethylhexafluorophosphate, triethyloxonium tetrafluoroborate or acetyl perchlorate. Polymerization can be carried out in bulk, suspension or solution polymerization. In order to remove unstable components, the copolymer is advantageously subjected to partial decomposition, either thermally or hydrolytically, until primary alcohol end groups are obtained (see US Pat. No. 3,103,499).
3219623).

The formaldehyde or trioxane homopolymers used according to the invention are likewise prepared in known manner by catalytic polymerization of monomers (see, for example, US Pat. Nos. 2,768,994 and 2,989,505).

Fibrids according to the invention are typically about 0.1
It has an irregular length of between 5 mm and preferably between 0.2 and 2 mm. The cross-sections are similarly irregular in shape and size, with apparent diameters typically ranging from about 1 to 200 μm.
m is preferably 2 to 50 μm.

Since the fibrids according to the invention are highly branched, they also have a high specific surface area (using argon according to the BET method) of 50 to 200 m 2 /g, preferably 70 m ² /g.
to 110 m ² /g, the sample being previously dried by freeze-drying. The degree of freeness is correspondingly high,
30 to 80°R, preferably 40 to 70°SR. The degree of freeness is determined by "Der Verein der Zellstoffand Papier".
It is determined as the Schopper-Riegler value according to the leaflet V/7/61 of ``Chemiker and Ingenieure'' (previous edition 107, published July 1, 1961).

The polyoxymethylene fibrids according to the invention have hydrophilic surface properties and can therefore be easily dispersed in water - often also without wetting agents. Filters made from this have improved adsorption properties. In special cases it may also be advantageous to produce a hydrophobic surface by adding suitable hydrophobes.

Due to its branched morphology, the fibrids according to the invention can be prepared in a known manner, for example as described in the German Patent Specification No.
It can be very well processed into paper as described in No. 1290040. The strengths of this pure polyoxymethylene paper (tear strength, initial wet strength, surface strength, Z-tear strength, fold strength) are in this case superior to those of the corresponding papers according to the state of the art. For example, fibrids according to the present invention or Rapid-Ko¨then
The tear strength of the paper sheet produced in the sheet forming apparatus is 2 to 25 N/mm ² , preferably 4 to 20 N/mm ² and especially 7 to 17 N/mm ² (sheet weight 160 g/m ² ,
(measured with an Instron sample testing machine at a sample width of 15 mm, elongation rate of 10 mm/min, and length measurement of 100 mm).
Measurements are carried out at 23°C and 50% relative humidity.

Mixing with other fibrous materials such as cellulose, cellulose fibers and synthetic fibers can also produce excellent papers, which can be smoothed, coated, laminated and printed in the usual manner. The strength of this mixed paper is also significantly higher than comparable papers made of known polyoxymethylene fibrids.

POM fibrids according to the invention can be used, for example, for wallpaper,
It can be used for filters, labels, graph paper and other special papers, etc. Polyoxymethylene fibrids can also be processed in cardboard machines, and the paper obtained has excellent resistance to water. Furthermore, the polyoxymethylene fibrids according to the invention can be used in non-woven fabrics and as glues in fast-curing kaltbits, dyes, plasters, adhesives, sealants and paints (unsaturated polyesters, epoxide resins, pigments). paste and
(based on PVC-plastisol).

In the process according to the invention for preparing fibrids, the known flash evaporation of a superheated and pressurized polymer solution into a low-pressure region is carried out, for example as described in Belgian Patent Specification No. 568,524. .

For this purpose, a homogeneous polymer solution is preferably first prepared, which depending on the preparation process can start from a dry or solvent-wet powder or granules, and the polymer is mixed with a solvent and, for example, in a pressurized autoclave. Heating is carried out under stirring, for example by steam jacket heating or by blowing steam. If the polyoxymethylene is obtained as a solution or suspension in an alcohol/water mixture of the composition according to the invention during the polymerization or during the subsequent stabilization and work-up process, the liquid can also be directly processed according to the invention. It can also be used directly in the method.

According to the invention - as already disclosed - a mixture is used consisting of 50-95% by weight of lower alcohols having 1-4 C atoms and 5-50% by weight of water, respectively, based on the total solvent. For this purpose, the lower alcohols used are, for example, methanol, ethanol, isopropanol, n-propanol, n-butanol, i-butanol or tert-butanol or mixtures of these alcohols. If more than four higher alcohols, such as n-hexanol, are used, fibrids are also obtained, but the temperatures required to produce the solution are then relatively high. In particular methanol and isopropanol are used.

The ratio of alcohol and water is extremely important for fibrid production. For example, if less than 50% by weight of lower alcohol and more than 50% by weight of water are used, plexus filaments will easily form. The boundary between the fibrids and the plexus filaments is of course not constant and can still be influenced to some extent by the choice of temperature and concentration of the solution, by the choice of the molecular weight and by the dimensions of the nozzle and the height of the pressure in the expansion zone. can give.

As the temperature increases, the polymer concentration decreases and the molecular weight decreases, as does the nozzle length/diameter ratio increase and the pressure in the expansion zone decreases, this boundary shifts more or less toward the watery side. If more than 95% lower alcohol and less than 5% water are used, the required solution temperature is often uneconomically high. A mixture consisting of 45-10% by weight of water and 55-90% by weight of lower alcohol is preferred.

The concentration of polymer in the solvent mixture is typically 10 to 300 g, preferably 50 to 200 g per solution. Lower concentrations are usually uneconomical. This is because it requires high solvent circulation. Higher concentrations often involve the risk of plexus filament formation. In this case, the upper limit of the polymer concentration depends to some extent on the molecular weight, the lower the molecular weight, the higher the permissible concentration.

The concentration of the polyoxymethylene solution depends on the molecular weight of the polymer, the type and amount of comonomer, and the solvent composition. While the lower temperature limit - as long as a homogeneous solution is used - is accepted as the required melting temperature, the upper temperature limit is limited primarily only by economic considerations. The melting temperature is known in many instances and can be easily modified by a person skilled in the art from data known in other cases or determined experimentally. In any case, the lower temperature limit must be such that sufficient evaporation for fibrid formation occurs at the selected pressure conditions in the expansion zone. This is usually the case if this is about 30° C. above the boiling point at normal pressure and at the same time the freezing point of the polymer is reached.
The preferred temperature range for the preferred alcohol at its preferred mixing ratio is 150 to 180°C.

The solution is usually under the inherent vapor pressure of the solvent mixture at this temperature, but this pressure can be increased significantly by inert gas pressure or by pumping. Generally the pressure is between 15 and 60 bar, preferably between 15 and 30 bar.

In addition to the polymer, the solution also contains polymeric auxiliaries such as those described in British Patent Specification No. 1146649, German Patent Application No. 1595705 and No. 1595668 and German Patent Application No. 1199504 and No. 1175882. decomposition products of catalysts for cationic polymerization such as Secondary alkali phosphates such as disodium hydrogen phosphate (U.S. Pat. Nos. 3,174,948, 3,219,623 and
3666714)) and the resulting reaction products such as methylal, trioxane, tetrooxane,
It can contain formic acid and methyl formate.

Furthermore, the polymer solution can contain a wide variety of known additives. These include, for example, common nucleating agents such as branched or reticulated polyoxymethylenes, talc or boron nitride, which promote crystallization and can be used to influence the morphology of the fibrids. (German Patent Specification No. 2101817, German Patent Application Publication No. 1940132)
(see issue).

Furthermore, known stabilizers against heat, oxygen and/or light (for example German Patent Application No.
2043498). For this purpose, especially bisphenol compounds,
Alkaline earth salts of carboxylic acids as well as guanidine compounds are suitable. Bisphenol compounds are mainly monobasic 4-hydroxyphenylalkanoic acids mono- or di-substituted in the nucleus by alkyl residues containing 1-4 carbon atoms (this is
-13 preferably containing 7, 8 or 9 carbon atoms) such as ω-(3-tert-butyl-
4-Hydroxyphenyl)-pentanoic acid, β-(3
-Methyl-5-tert-butyl-4-hydroxyphenyl)-propionic acid, (3,5-di-tert-butyl-
4-hydroxyphenyl)-acetic acid, β-(3,5-
tert-butyl-4-hydroxyphenyl)-propionic acid or (3,5-diisopropyl-4-hydroxyphenyl)-acetic acid and ethylene glycol,
Propanediol-(1,2), propanediol-(1,3), butanediol-(1,4), hexanediol-(1,6), 1,1,1-trimethylolethane or pentaerythritol esters are used.

As the alkaline earth salt of carboxylic acid, especially 2-
20 Alkaline earth salts of aliphatic, preferably mono-, di- or tribasic carboxylic acids containing hydroxy groups, preferably having 3-9 carbon atoms, such as stearic acid, ricinoleic acid, lactic acid, maldic acid, malic acid or citric acid. Calcium or magnesium salts are used.

As a guanidine compound, the formula (wherein R means a hydrogen atom, a cyano group or an alkyl residue having 1 to 6 carbon atoms) such as cyanoguanidine, N-cyano-N-
Cyano-N'-methylguanidine, N-cyano-
N'-ethylguanidine, N-cyano-N'-isopropylguanidine, N-cyano-N'-tert-butylguanidine or N,N'-dicyanoguanidine are used. Guanidine compound optionally 0.01-1% preferably 0.02-0.5% by weight based on the total weight
used in amounts of

Furthermore, the solution can also contain further additives, such as known antistatic agents, flame retardants or lubricants.

Filled fibrids are obtained according to the invention by homogeneously suspending the mineral filler in a polymer solution and then carrying out as described.
Suitable pigments in this case are titanium dioxide, calcium carbonate, talc, wollastonite, dolomite, silicon dioxide, etc.

The colored polyoxymethylene fibrids are capable of dissolving or dispersing the dye in the polymer solution. The addition of fluorescent brighteners is also of interest for some uses.

To improve the dispersibility of the polyoxymethylene fibrids, surfactants such as oxyethylated alcohols, carboxylic acids or amines, alkanesulfonates or polymers containing hydroxyl groups such as polyvinyl alcohol or carboxymethyl cellulose can also be added to the solution. can.

The polymer solution is then forced through one or more nozzles. The design of the nozzle (size, shape and length) will certainly influence the dimensions of the fibrids produced and can alter the concentration limits of the indicated solvent mixture somewhat, but is not critical to the invention. Suitable nozzles are described, for example, in Belgian Patent Specification No. 568,524. Here the diameter for example
Mention may be made of simple nozzles with a length of 0.5-5 mm and a length of 0.1 to 1000 cm, circular nozzles with a comparable annular gap, and bimaterial nozzles, in which case an inert gas such as nitrogen, water vapor, etc. or a liquid such as superheated water is used as the propellant medium. can be used.

The polymer solution is passed through a nozzle into a low pressure area where the solvent evaporates completely or partially. In this case, it is also possible before the solution is removed from the nozzle to subject it to a controlled release of pressure, for example by passing it through a chamber or a tube having a larger diameter than the nozzle outlet. Any remaining lower alcohols present can be removed, for example, by steam. Typically, the low pressure area is a closed vessel from which solvent vapors are removed by a pump. It can be returned to the process after condensation. The pressure in the low pressure range is between 0.02 bar and 2.0 bar, preferably between 0.1 and 1 bar.
It's a crowbar.

The fibrids are subsequently removed by known mechanical methods such as suction filtration, centrifugation, etc. to remove most of the unevaporated solvent, washed if necessary with water and then supplied for use in wet form. Range is 10 to
It is loosened to a density of 200 g/preferably 30 to 100 g/and subsequently dried in a hot gas stream.

A significant advantage of the process according to the invention is that fibrids are obtained immediately upon atomization, thereby avoiding a complicated and energy-intensive two-step process consisting of the production of infinitely long plexus filaments and subsequent mechanical comminution. That's true. Since the plexus filaments have a high elongation rate, this mechanical comminution can only be carried out with high energy consumption. The advantages of this method as well as the material advantages of the polyoxymethylene fibrids according to the invention were unexpected and therefore surprising.

The invention will be explained in detail by the following example.

Example 1 In a pressurizer with a volume of 70 and a multistage five-impeller countercurrent stirrer, a mixture of 98% by weight trioxane and 2% by weight ethylene oxide with an RSV-value of 0.82
2 kg of copolymer with dl/g and 20 ml of triethylamine are dissolved in a mixture of 13 methanol and 7 parts water. A total pressure of 30 bar is achieved with nitrogen. After opening the bottom valve, the solution is passed through a single-hole nozzle with a diameter of 1 mm and a length of approximately 0.5 mm, with a capacity of 200 mm.
and fill with water 40 and vacuum pump
Flow into a gas chamber in a closed receiver that guarantees a pressure of 0.8 bar. After the end of atomization, the methanol is driven off by purging with steam and for 30 minutes while maintaining a pressure of 0.8 bar. The resulting fibrid suspension is removed via the bottom valve and centrifuged to a solids content of approximately 20%.

To determine the specific surface area of the fibrids obtained, the samples are lyophilized and determined by the BET method using argon. The specific surface area is 73 m ² /g, and the degree of beating is 50°SR.

Furthermore, as an indirect measurement of fiber length distribution, Brecht Holl
In this device, 2 g of fibers are sequentially separated into various sizes by means of a water jet pump for 10 minutes using a water pressure of 0.5 bar and a pulsating suction membrane (with as large a stroke as possible). Wash through a sieve. The residue on the sieves with mesh widths of 1.2 mm, 0.4 mm and 0.12 mm and the through-through are expressed as percentages.

The following fractions are measured in the above fiber classification: Residue 1.2mm: 0% Residue 0.4mm: 17% Residue 0.12mm: 54% Passage 0.12mm: 29% Rapid - Produce paper sheets of 160 g/m ² on a Ko¨then sheet forming machine. The tear strength measured on this sheet is 14.3 N/mm ² .

Comparative Test 1 As described in Example 1, the same copolymer was dissolved in methyl ethyl ketone 20 under the same temperature and pressure conditions and atomized into the same container through the same nozzle, also at a pressure of 0.8 bar. keep it.
The resulting product consists exclusively of continuous plexus filaments, which in this form is not suitable for paper production. The sample is therefore milled in 6 passes through a disc refiner. Measurements of the fibrids produced in this manner show the following values.

Specific surface area: 39m ² /g Beating degree: 27゜SR Fiber classification: Residue 1.2mm: 3% Residue 0.4mm: 4% Residue 0.12mm: 26% Passage: 67% Sheet tear strength (160g/m ² ): 0.37 N/mm ² Even if the polymer concentration is lowered to 0.01 Kg/, plexi filaments unsuitable for paper production are obtained.

Comparative Test 2 Carry out as in Example 1. However, the solvent composition was 15 parts methanol and 5 parts water. In this form, exclusively plexi filaments are obtained which are unsuitable for paper production.

Example 2 Perform as in Example 1. The RSV value of the polymer used was 1.0 dl/g and the solvent composition was 15 parts methanol and 5 parts water. The measured values for the fibrids obtained are as follows: Specific surface area: 98 m ² /g Beatness: 61°SR Fiber classification: Residue 1.2 mm: 0% Residue 0.4 mm: 5% Residue 0.12 mm : 55% Passage: 0.12 mm : 40% Tear strength of paper: 13.2 N/mm ² Examples 3 Proceed as in Example 1, but using isopropanol instead of methanol. The measured values for the fibrids obtained are as follows: Specific surface area: 108 m ² /g Beatness: 68°SR Fiber classification: Residue 1.2 mm: 6% Residue 0.4 mm: 4% Residue 0.12 mm : 24% Passage: 0.12mm : 66% Paper tear strength : 11.7N/mm ²

Claims (1)

[Scope of Claims] 1 Consists of a homopolymer of formaldehyde or a cyclic oligomer of formaldehyde, or a copolymer of formaldehyde or a cyclic oligomer of formaldehyde, in which case it contains at least two carbon atoms in addition to the oxymethylene unit. The copolymer contains another oxyalkylene unit having primary alcohol end groups, the heated solution of the polymer containing 55-90% by weight of lower alcohol and 10-45% by weight of water as solvent. A polyoxymethylene fibride having a converted specific viscosity of 0.4 to 2.0 dl/g, a specific surface area of 50 to 200 m ² /g and a beating degree of 30 to 80° SR, formed by flash evaporation in the presence of a mixture consisting of: 2. The polyoxymethylene fibride according to claim 1, having a specific surface area of 70 to 110 m ² /g. 3. The polyoxymethylene fibride according to claim 1 or 2, which has a freeness of 40 to 70°SR. 4 A heated solution of the polymer is flash evaporated through a nozzle into a low pressure area to produce a homopolymer of formaldehyde or a cyclic oligomer of formaldehyde, or a copolymer of formaldehyde or a cyclic oligomer of formaldehyde, in which case oxymethylene units are obtained. and at least 2
further oxyalkylene units having 5 carbon atoms, the copolymer having primary alcohol end groups and a reduced specific viscosity of 0.4 to 2.0 dl/
g, specific surface area 50 to 200 m ² /g, and freeness 30 to 30.
To prepare polyoxymethylene fibrids with an SR of 80°, 50-95% by weight of lower alcohols having 1-4 C-atoms and 5-95% of water are used as solvents.
A manufacturing method, characterized in that a mixture consisting of 50% by weight is used. 5. The method according to claim 4, wherein methanol or isopropanol is used as the alcohol. 6. The method according to claim 4 or 5, wherein a mixture of 55 to 90% by weight of lower alcohol and 10 to 45% by weight of water is used as the solvent.